Controls on Organic Carbon Burial in the Eastern China Marginal Seas: A Regional Synthesis

Abstract

Marginal seas are important burial centers of both marine and terrestrial organic carbon (OC), accounting for the burial of more than 90% of sedimentary OC in marine environments Burdige, 2005;Hedges & Keil, 1995). These marginal seas receive vast amounts of sediments, freshwater, and nutrients from their adjacent rivers and coastal erosion, especially in those large delta-front estuaries (Bianchi & Allison, 2009;Kuehl et al., 2020). Large seasonal shifts of terrigenous inputs impact sedimentation rates, sources/age of OC, and primary productivity -all critical in controlling burial and decomposition of OC in marginal seas (Bauer et al., 2013;Bianchi et al., 2014;Liu et al., 2010). Recent work on differentiation of rock-derived or petrogenic OC (OC petro ) from physical erosion of bedrock in river drainage basins Abstract A regional synthesis of organic carbon (OC) burial was conducted using a comprehensive data set to reveal some of the key drivers and human multi-stressors controlling OC burial and transport in the Eastern China Marginal Seas (ECMS). Both OC and Δ 14 C values of suspended particulate matter (SPM) in the Changjiang River, were significantly higher than estuarine mobile-muds, suggesting selective decay of more labile younger OC from both marine and terrestrial sources and the accumulation of more recalcitrant older OC. Some of this decay is likely to be associated with iron-redox cycling in mobile-muds. In contrast, OC, δ 13 C, and Δ 14 C values increased along the Yellow River sediment dispersal pathway, indicating adding of young marine OC and less decay of terrestrial OC. OC burial efficiency in mud areas in the Bohai Sea (∼43%) was significantly higher than those in the Yellow (∼11%) and East China Seas (∼16%), owing to rapid deposition. Burial flux of biospheric OC in mud areas of the ECMS is 7.00 ± 0.79 Mt yr −1 , corresponding to atmospheric CO 2 drawdown by silicate weathering in major river drainage basins of mainland China. The burial flux of petrogenic OC was estimated to be 0.81 ± 0.25 Mt yr −1 , accounting for >1.9% of total burial in the global ocean. While the ECMS is an important OC sink, river damming has greatly reduced OC burial. Thus, the overall impact on anthropogenically altered riverdominated marginal seas remains an important and rapidly changing component of the coastal ocean carbon budget.Plain Language Summary A comprehensive regional synthesis of organic carbon (OC) burial and its drivers, were investigated across the Eastern China Marginal Seas (ECMS). Variation of OC content and carbon isotopic composition from suspended particulate matter to mobile muds, in Changjiang sediment dispersal pathways, indicated selective decomposition of younger more labile marine and terrestrial OC, which resulted in the accumulation of older more recalcitrant OC. However, continuous adding of young marine OC, with little loss of terrestrial OC, in Yellow River sediment dispersal pathway, resulted in more recalcitrant terrestrial OC buried in this relatively more quiescent sedimentary ...

The Sources and Burial of Marine Organic Carbon in the Eastern China Marginal Seas

“…Our proto-burial efficiency estimates are broadly comparable to previous findings from the ECMS, but there are also major differences. For example, an average burial efficiency of 11% has been reported for the mud areas of ECMS (Zhao et al, 2021). Another study found a burial efficiency of 10% in the whole ECS (Duan et al, 2017) and 14% in the mud areas of the ECS (Zhao et al, 2021).…”

“…Most lipid biomarker data were collected from previous studies (n = 227 for surface suspended particles, and n = 258 for surface sediments) (Zhang et al, 2008;Jiang et al, 2012;Tao et al, 2012;Zhao et al, 2013;Fan et al, 2014aFan et al, ,b, 2015Xing et al, 2014Xing et al, , 2016aHu J. et al, 2016;Wu et al, 2016;Wang et al, 2019), while some were measured in this study, i.e., marine lipid biomarkers in surface suspended particles from the BS and northern YS in the June of 2011, part of the samples in the ECS and southern YS in June of 2010 and July of 2013, respectively, and the CRE in July of 2013 (n = 107). In addition, most data of the following parameters were collected from published results: sea surface temperature (n = 273, from five cruises in summer of 2010-2015), salinity (n = 273, from five cruises in summer of 2010-2015), nutrient concentrations [dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and silicate (Si)] (n = 133, from three cruises in summer of 2011 and 2015) and Chl a (n = 255, from five cruises in summer of 2010-2014) in the surface water (Jiang et al, 2012;Yang et al, 2015;Hu J. et al, 2016;Wu et al, 2016;Tian et al, 2019;Wang et al, 2019), as well as terrestrial biomarker [ (C 27 + C 29 + C 31 ) n-alkanes] contents (n = 226), TOC (n = 200), δ 13 C TOC , mean grain size and sedimentation rate in surface sediments (Zhao et al, 2011(Zhao et al, , 2013(Zhao et al, , 2021Jiang et al, 2012;Tao et al, 2012;Fan et al, 2014aFan et al, ,b, 2015Xing et al, 2014Xing et al, , 2015Xing et al, , 2016aBao et al, 2016;Qiao et al, 2017). Some data were measured using in situ CTD instrument in this study: sea surface temperature and salinity in the ECS in June 2010 and July 2013 (n = 54), and Chl a in the YRE in August 2015 (n = 33).…”

“…Note that MOC and TOC in this study are expressed as percentage of dry weight. To calculate the relative contribution of marine OC (f Mar ) using δ 13 C TOC , a global average value of −20.0 was selected as the marine end-member (X Mar ) in our study, which is the most widely used marine end-member in previous studies (Zhang et al, 2007;Weijers et al, 2009;Wang J. et al, 2015;Zhao et al, 2021). The average value of δ 13 C POC in the modern Yellow River is −26.5 (Cai et al, 2003).…”

“…It has been revealed that the global marine OC burial is about 100 Tg C yr −1 , being about two times higher than that of terrestrial OC (Burdige, 2005). Previous studies have focused on the sources and burial processes of terrestrial OC (Burdige, 2005;Karlsson et al, 2011;Fang et al, 2015;Smith et al, 2015;Zhao et al, 2021), while these processes of marine OC in marginal seas have not been fully understood.…”

“…Zhang H. et al (2017) also found that the satellite-derived surface Chl a from 2000 to 2012 was the highest in summer in the BS. The common methods to study the burial of marine OC include measurements of total organic carbon (TOC) combined with isotopes of C and N, biogenic silica and pigments in sediments (Liu et al, 2015;Wang L. et al, 2015;Yoon et al, 2016;Zhao et al, 2021). In the BS, the high content of marine OC calculated by δ 13 C and biogenic silica was located in fine-grain sediments, with an important contribution of authigenic OC derived from primary productivity at the upper layers, while the values were low in the Bohai Strait with coarse grain deposition (Liu et al, 2015).…”